As announced in our previous report, we have expanded the scope of our investigation of neuroborreliosis in the rhesus monkey, in pursuit of signs of central nervous system (CNS) involvement. Nine additional animals were purchased. Five were inoculated with a neurotropic strain of B. burgdorferi (NT1). One animal was left uninfected, as a control, and the remaining 3 were infected with the JD1 strain that we had used before. We are searching longitudinally for the appearance of signs of both PNS and CNS involvement. Signs of PNS involvement are sought for, as before, by nerve conduction measurements. CNS involvement is investigated by looking for pleocytosis in the CSF and by evoked potential studies. At this writing, none of the animals has shown signs of PNS involvement but there is a preliminary indication that one animal has signs of CNS involvement, as judged by measurements of evoked potentials. Moreover, several of the infected animals have shown pleocytosis in their CSF. Pleocytosis was present in animals infected with either strain, but it appears to be more intense and long-lasting in animals infected with NT1. Infection was demonstrated in all but one of the inoculated animals by in vitro culture of skin biopsy samples, and in all of the inoculated animals by Western blot.